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[InstCombine] Add more cases for simplifying (icmp (and/or x, Mask), y) #85138

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[InstCombine] Add more cases for simplifying (icmp (and/or x, Mask), y) #85138

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b1f57be
[InstCombine] Add more tests for simplifying `(icmp (and/or x, Mask),…
goldsteinn Mar 13, 2024
ab8ac21
[InstCombine] Add more cases for simplifying `(icmp (and/or x, Mask),…
goldsteinn Mar 13, 2024
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152 changes: 98 additions & 54 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -4177,7 +4177,9 @@ static bool isMaskOrZero(const Value *V, bool Not, const SimplifyQuery &Q,
/// a check for a lossy truncation.
/// Folds:
/// icmp SrcPred (x & Mask), x to icmp DstPred x, Mask
/// icmp SrcPred (x & ~Mask), ~Mask to icmp DstPred x, ~Mask
/// icmp eq/ne (x & ~Mask), 0 to icmp DstPred x, Mask
/// icmp eq/ne (~x | Mask), -1 to icmp DstPred x, Mask
/// Where Mask is some pattern that produces all-ones in low bits:
/// (-1 >> y)
/// ((-1 << y) >> y) <- non-canonical, has extra uses
Expand All @@ -4189,82 +4191,126 @@ static bool isMaskOrZero(const Value *V, bool Not, const SimplifyQuery &Q,
static Value *foldICmpWithLowBitMaskedVal(ICmpInst::Predicate Pred, Value *Op0,
Value *Op1, const SimplifyQuery &Q,
InstCombiner &IC) {
Value *X, *M;
bool NeedsNot = false;

auto CheckMask = [&](Value *V, bool Not) {
if (ICmpInst::isSigned(Pred) && !match(V, m_ImmConstant()))
return false;
return isMaskOrZero(V, Not, Q);
};

if (match(Op0, m_c_And(m_Specific(Op1), m_Value(M))) &&
CheckMask(M, /*Not*/ false)) {
X = Op1;
} else if (match(Op1, m_Zero()) && ICmpInst::isEquality(Pred) &&
match(Op0, m_OneUse(m_And(m_Value(X), m_Value(M))))) {
NeedsNot = true;
if (IC.isFreeToInvert(X, X->hasOneUse()) && CheckMask(X, /*Not*/ true))
std::swap(X, M);
else if (!IC.isFreeToInvert(M, M->hasOneUse()) ||
!CheckMask(M, /*Not*/ true))
return nullptr;
} else {
return nullptr;
}

ICmpInst::Predicate DstPred;
switch (Pred) {
case ICmpInst::Predicate::ICMP_EQ:
// x & (-1 >> y) == x -> x u<= (-1 >> y)
// x & Mask == x
// x & ~Mask == 0
// ~x | Mask == -1
// -> x u<= Mask
// x & ~Mask == ~Mask
// -> ~Mask u<= x
DstPred = ICmpInst::Predicate::ICMP_ULE;
break;
case ICmpInst::Predicate::ICMP_NE:
// x & (-1 >> y) != x -> x u> (-1 >> y)
// x & Mask != x
// x & ~Mask != 0
// ~x | Mask != -1
// -> x u> Mask
// x & ~Mask != ~Mask
// -> ~Mask u> x
DstPred = ICmpInst::Predicate::ICMP_UGT;
break;
case ICmpInst::Predicate::ICMP_ULT:
// x & (-1 >> y) u< x -> x u> (-1 >> y)
// x u> x & (-1 >> y) -> x u> (-1 >> y)
// x & Mask u< x
// -> x u> Mask
// x & ~Mask u< ~Mask
// -> ~Mask u> x
DstPred = ICmpInst::Predicate::ICMP_UGT;
break;
case ICmpInst::Predicate::ICMP_UGE:
// x & (-1 >> y) u>= x -> x u<= (-1 >> y)
// x u<= x & (-1 >> y) -> x u<= (-1 >> y)
// x & Mask u>= x
// -> x u<= Mask
// x & ~Mask u>= ~Mask
// -> ~Mask u<= x
DstPred = ICmpInst::Predicate::ICMP_ULE;
break;
case ICmpInst::Predicate::ICMP_SLT:
// x & (-1 >> y) s< x -> x s> (-1 >> y)
// x s> x & (-1 >> y) -> x s> (-1 >> y)
if (!match(M, m_Constant())) // Can not do this fold with non-constant.
return nullptr;
if (!match(M, m_NonNegative())) // Must not have any -1 vector elements.
return nullptr;
// x & Mask s< x [iff Mask s>= 0]
// -> x s> Mask
// x & ~Mask s< ~Mask [iff ~Mask != 0]
// -> ~Mask s> x
DstPred = ICmpInst::Predicate::ICMP_SGT;
break;
case ICmpInst::Predicate::ICMP_SGE:
// x & (-1 >> y) s>= x -> x s<= (-1 >> y)
// x s<= x & (-1 >> y) -> x s<= (-1 >> y)
if (!match(M, m_Constant())) // Can not do this fold with non-constant.
return nullptr;
if (!match(M, m_NonNegative())) // Must not have any -1 vector elements.
return nullptr;
// x & Mask s>= x [iff Mask s>= 0]
// -> x s<= Mask
// x & ~Mask s>= ~Mask [iff ~Mask != 0]
// -> ~Mask s<= x
DstPred = ICmpInst::Predicate::ICMP_SLE;
break;
case ICmpInst::Predicate::ICMP_SGT:
case ICmpInst::Predicate::ICMP_SLE:
return nullptr;
case ICmpInst::Predicate::ICMP_UGT:
case ICmpInst::Predicate::ICMP_ULE:
llvm_unreachable("Instsimplify took care of commut. variant");
break;
default:
llvm_unreachable("All possible folds are handled.");
// We don't support sgt,sle
// ult/ugt are simplified to true/false respectively.
return nullptr;
}

// The mask value may be a vector constant that has undefined elements. But it
// may not be safe to propagate those undefs into the new compare, so replace
// those elements by copying an existing, defined, and safe scalar constant.
Value *X, *M;
// Put search code in lambda for early positive returns.
auto IsLowBitMask = [&]() {
if (match(Op0, m_c_And(m_Specific(Op1), m_Value(M)))) {
X = Op1;
// Look for: x & Mask pred x
if (isMaskOrZero(M, /*Not=*/false, Q)) {
return !ICmpInst::isSigned(Pred) ||
(match(M, m_NonNegative()) || isKnownNonNegative(M, Q));
}

// Look for: x & ~Mask pred ~Mask
if (isMaskOrZero(X, /*Not=*/true, Q)) {
return !ICmpInst::isSigned(Pred) ||
isKnownNonZero(X, Q.DL, /*Depth=*/0, Q.AC, Q.CxtI, Q.DT);
}
return false;
}
if (ICmpInst::isEquality(Pred) && match(Op1, m_AllOnes()) &&
match(Op0, m_OneUse(m_Or(m_Value(X), m_Value(M))))) {

auto Check = [&]() {
// Look for: ~x | Mask == -1
if (isMaskOrZero(M, /*Not=*/false, Q)) {
if (Value *NotX =
IC.getFreelyInverted(X, X->hasOneUse(), &IC.Builder)) {
X = NotX;
return true;
}
}
return false;
};
if (Check())
return true;
std::swap(X, M);
return Check();
}
if (ICmpInst::isEquality(Pred) && match(Op1, m_Zero()) &&
match(Op0, m_OneUse(m_And(m_Value(X), m_Value(M))))) {
auto Check = [&]() {
// Look for: x & ~Mask == 0
if (isMaskOrZero(M, /*Not=*/true, Q)) {
if (Value *NotM =
IC.getFreelyInverted(M, M->hasOneUse(), &IC.Builder)) {
M = NotM;
return true;
}
}
return false;
};
if (Check())
return true;
std::swap(X, M);
return Check();
}
return false;
};

if (!IsLowBitMask())
return nullptr;

// The mask value may be a vector constant that has undefined elements. But
// it may not be safe to propagate those undefs into the new compare, so
// replace those elements by copying an existing, defined, and safe scalar
// constant.
Type *OpTy = M->getType();
auto *VecC = dyn_cast<Constant>(M);
auto *OpVTy = dyn_cast<FixedVectorType>(OpTy);
Expand All @@ -4280,8 +4326,6 @@ static Value *foldICmpWithLowBitMaskedVal(ICmpInst::Predicate Pred, Value *Op0,
M = Constant::replaceUndefsWith(VecC, SafeReplacementConstant);
}

if (NeedsNot)
M = IC.Builder.CreateNot(M);
return IC.Builder.CreateICmp(DstPred, X, M);
}

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